Dobson highlighted Vander Plaats's opposition to gay marriage in a statement announcing his support: "Bob has fought tirelessly for conservative family values. He is passionately pro-life and supports the exclusivity of marriage between one man and one woman. Vander Plaats believes that all voters, not just one liberal court, should decide what the definition of marriage should be."

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Vander Plaats is an underdog in Tuesday's election, trailing former four-term Gov. Terry Branstad in public polls of the race. A Public Policy Polling survey released this week showed Branstad ahead by 15 percentage points.

Vander Plaats has relied on his strength among religious conservatives throughout the campaign, picking up an endorsement from Arkansas Gov. Mike Huckabee, whose Iowa campaign he chaired during the 2008 presidential election. Vander Plaats is also pulling a leaf from Huckabee's Iowa playbook this weekend, bringing in actor and martial-arts guru Chuck Norris for a campaign swing.

Both Branstad and Vander Plaats have led sitting Democratic Gov. Chet Culver in several general election polls.